This inventions concerns a process for the manufacture of certain fluorocarbons which have an olefinic bond by defluorination of a fluorocarbon starting material having a corresponding saturated bond.
Fluorinated olefins are used to prepare fluoropolymers. These polymers typically have a unique combination of properties. These include inter alia high thermal stability, chemical inertness, unusual surface properties, low dielectric constant and low flammability.
2-Trifluoromethyl-3,3,3-trifluoropropene (i.e., (CF3)2Cxe2x95x90CH2 or HFIB) is an example of a fluoroolefin that has been used to prepare various polymers. For example, it has been copolymerized with vinylidene fluoride to produce an alternating copolymer having exceptional thermal, chemical and mechanical properties. Numerous routes to HFIB have been disclosed. For example, U.S. Pat. No. 4,705,904 discloses the manufacture of HFIB by reacting hexafluoroacetone or hexafluoropropylene oxide, its precursor, with ketene or a ketene precursor at 500xc2x0 C. to 700xc2x0 C. Traces of perfluoroisobutylene, a highly toxic olefin, are found in the crude product mixture. U.S. Pat. No. 4,766,238 discloses a process for the preparation of HFIB by the reaction of monochloromethyl 2-trifluoromethyl-3,3,3-trifluoropropionate with an amine. The propionate ester is prepared by chlorination of the methyl ester. The use of chlorine or chlorine-containing precursors presents a waste disposal problem. Further disadvantages of the art processes are described in U.S. Pat. No. 4,705,904.
U.S. Pat. No. 4,820,884 discloses a process for preparing an unsaturated aliphatic or cycloaliphatic perfluorocarbon having at least six carbon atoms and having at least one carbon-carbon double bond comprising contacting the corresponding perfluoroalkane or perfluorocycloalkane having at least two adjacent tertiary carbon atoms with activated carbon at a temperature of from about 300xc2x0 C. to about 500xc2x0 C.
There is an interest in developing more efficient processes for the manufacture of unsaturated fluorocarbons, particularly, fluorinated olefins. Furthermore, the unsaturated fluorocarbons prepared by the process of this invention also contain hydrogen. These compounds, unlike perfluorinated unsaturated fluorocarbons, pose less of an environmental problem and are typically less expensive than their perfluorinated analogues.
A process is provided for producing an olefinic fluorocarbon selected from the group consisting of (CF3)2Cxe2x95x90CH2, CF3CHxe2x95x90CF2, CF2xe2x95x90C(CF3)OCF2CHF2 and C6H5C(CF3)xe2x95x90CF2. The process comprises contacting the corresponding fluorocarbon starting material selected from the group consisting of (CF3)2CFCH2F, (CF3)2CHF, (CF3)2CFOCF2CHF2 and C6H5CF(CF3)2, in the vapor phase, with a defluorination reagent selected from the group consisting of carbon, copper, iron, nickel and zinc at an elevated temperature of at least 300xc2x0 C.
In accordance with the process of this invention, certain hydrogen-containing fluorocarbon starting materials surprisingly defluorinate (i.e., lose two fluorine atoms) rather than dehydrofluorinate (i.e., lose hydrogen fluoride). In particular, it has been found that (CF3)2Cxe2x95x90CH2 can be produced from (CF3)2CFCH2F; CF3CHxe2x95x90CF2 can be produced from (CF3)2CHF; CF2xe2x95x90C(CF3)OCF2CHF2 can be produced from (CF3)2CFOCF2CHF2; and 
can be produced from 
(CF3)2CFCH2F can be prepared by the reaction of difluoromethane, antimony pentafluoride and perfluoropropylene in an autoclave at 80xc2x0 C. Further details are described in International Publication No. WO 98/42645. (CF3)2CHF (227ea) can be prepared by the addition of HF to hexafluoropropene in the presence of activated carbon as described in British Patent Specification No. 902,590. (CF3)2CFOCF2CHF2 is a known compound (see Example 7). C6H5CF(CF3)2 can be prepared by a procedure described in W. A. Sheppard, J. Am. Chem. Soc., 87, 2410 (1965).
The carbon defluorination reagent includes activated carbon and acid-washed carbons (e.g., carbons which have been treated with hydrochloric acid or hydrochloric acid followed by hydrofluoric acid). Suitable acid treatment of carbons is described in U.S. Pat. No. 5,136,113. The carbon catalyst also includes three dimensional matrix porous carbonaceous materials. Examples are those described in U.S. Pat. No. 4,978,649. Of note are three dimensional matrix carbonaceous materials which are obtained by introducing gaseous or vaporous carbon-containing compounds (e.g., hydrocarbons) into a mass of granules of a carbonaceous material (e.g., carbon black); decomposing the carbon-containing compounds to deposit carbon on the surface of the granules; and treating the resulting material with an activator gas comprising steam to provide a porous carbonaceous material. A carbon-carbon composite material is thus formed.
The carbon, copper, iron, nickel and zinc defluorination reagents can be in any convenient form such as powder, granules and chips. The iron and nickel reagents may also be in gauze form. The metal defluorination reagents (i.e., Cu, Fe, Ni and Zn) can be regenerated by reaction with hydrogen at temperatures of 300xc2x0 C. to 600xc2x0 C.
In the process of the invention a fluorocarbon starting material selected from (CF3)2CFCH2F, (CF3)2CHF, (CF3)2CFOCF2CHF2 and C6H5CF(CF3)2 is contacted with the defluorination reagent at a temperature of from about 300xc2x0 C. to about 800xc2x0 C., preferably from about 350xc2x0 C. to about 500xc2x0 C. The fluorocarbon starting material is reacted in the vapor phase and may be contacted with the defluorination reagent neat or diluted with an inert gas such as argon and nitrogen.
The contact time is typically from about 0.1 seconds to about 30 minutes.
The vapor phase process of this invention can be carried out using well-known chemical engineering practice. The process is conveniently done at atmospheric pressure, although subatmospheric or superatmospheric pressures can be employed. Reactor vessels of stainless steel are typically used although other materials such as nickel-based corrosion resistant alloys such as Hastelloy(trademark) nickel alloy can be used.
Without further elaboration, it is believed that one skilled in the art can, using the description herein, utilize the present invention to its fullest extent. The following specific embodiments are to be construed as illustrative, and not as constraining the remainder of the disclosure in any way whatsoever.